1. Field of the Invention
The invention relates to a current metering and abnormal event monitoring system (MMS) which can continuously monitor the current flow to electrical equipment, and in particular to an MMS current sensor assembly that can readily be installed in a variety of site configurations to accommodate different numbers of conductors, conductor sizes, and configurations.
The invention also relates to an MMS current sensor assembly of the invention with integrated self-calibration, processing, display, and/or communications capabilities that enable the sensor assembly to be used to monitor and alarm a wide variety of different power parameters, and whose individual components are arranged for installation, repair, and/or replacement with minimal downtime, thereby making the MMS current sensor assembly especially suitable for mission critical applications.
2. Description of Related Art
The rigorous demands of mission critical sites, like data centers, require close to “real time” methods of metering and monitoring, displaying and/or alarming of power parameters that could cause anomalies in the site mission. Since the MMS is a current “watch dog” of the mission critical production equipment, the accuracy must be great enough to detect any anomalies that would affect production costs or “thru-put”. The system should be accurate, and must have a minimum loss of data when repair is required.
System accuracy is important, by way of example, in the following power usage monitoring applications:                Billing of power used for leased space; power used is sometimes proportioned to current drawn.        Verification of equipment operation; increase or decrease of current metrics could indicate equipment failure or degradation.        Verification of redundant server operation; if one server goes “off line” the current to units of the redundant pair will be unbalanced.        
In addition to monitoring total power usage for billing or operation verification, the MMS may be required to check for power anomalies indicative of “abnormal events” such as:                Arcs that cause arc flash damage to equipment and injury to personnel.        Leakage currents to ground or other conductors, indicating potentially failing equipment.        Even current harmonics in AC power system which may indicate failing equipment.        Overload currents.        Current unbalances in redundant equipment indicating loss of redundancy.        Current dropping to near zero after being normal, indicating equipment failure.        
Thus, the current sensor must be able to respond both to rapid changes in current, even current harmonics (which include DC), large and small amplitude fluctuations, and so forth. This requires a high degree of flexibility, including a high current sensing bandwidth, and the ability to implement a wide variety of different current monitoring algorithms.
Individual sensors having sufficient bandwidth to monitor both AC and DC currents are known. One such sensor is disclosed in U.S. Pat. No. 7,298,132. However, sensors such as the one shown in U.S. Pat. No. 7,298,132 are difficult to install, because they require disconnection of the conductors to be monitored, and because they require complex calibration procedures that require a skilled operator. In addition, such individual sensors lack integrated processing, display, and communications capabilities.
Self-calibrating sensors are also known. One such sensor is disclosed in U.S. Pat. No. 6,734,661. Again, however, the known sensor is difficult to install and is relatively limited in application. For example, the sensor of U.S. Pat. No. 6,734,661 is exclusively an AC sensor, and thus cannot be used to monitor even harmonics or other conditions that may involve detection of DC currents.
A current sensor unit having an integrated signal processor for detecting electrical disturbances and for communicating data to a network is disclosed in U.S. Pat. No. 7,714,588. However, this sensor unit also lacks the ability to adapt to different wiring configurations and monitoring requirements.
Additional prior patents and publications directed to sensor units include U.S. Pat. No. 6,680,730, which discloses a current sensor having a clip member to facilitate mounting of the core on a conductor; U.S. Patent Publication No. 2009/0278526, which discloses a current sensor that includes Hall elements situated on a circuit board in an opening of a magnetic core surrounding a bus bar, with additional amplifier elements on the circuit board, and U.S. Pat. No. 7,265,531, which discloses a Hall effect current sensor and core that fit into specially designed recesses on opposite sides of a bus bar.
None of the prior current sensors offer a complete solution to the problem of current monitoring in mission critical applications, either because they are difficult to install, leading to increased downtime for repair or replacement, can only be installed on specific wiring configurations, necessitating the purchase and installation of multiple different current sensors for different purposes in a single installation, or lack sufficient bandwidth or processing/communication capabilities to carry out a full complement of monitoring and alarm functions.